Pneumatic tire

ABSTRACT

A pneumatic tire in which an inner liner including a film mainly made of thermoplastic resin is attached to an inside of the tire via a tie rubber sheet, on an inner side of a carcass layer, and which has a lap-splice portion where end portions of the film in a tire circumferential direction overlap each other in a tire widthwise direction with tie rubber therebetween. A section of the film on a tire cavity side in the lap-splice portion has a portion where the film is thin over part or entirety of the width in the tire widthwise direction before the lap-splice portion, or a film thickness in the lap-splice portion is smaller than a film thickness in a portion other than the lap-splice portion. Thus, the pneumatic tire has no crack developing around the lap-splice portion of an inner liner layer after running, and has excellent durability.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(a) to JapanesePatent Application No. 2012-001977, filed in Japan on Jan. 10, 2012 andJapanese Patent Application No. 2012-001992, filed in Japan on Jan. 10,2012, the entire contents of Japanese Patent Application Nos.2012-001977 and 2012-001992 are hereby incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a pneumatic tire. More specifically,the present invention relates to a pneumatic tire having an inner linerthat is configured to improve durability of the pneumatic tire.

2. Background Information

In recent years, it has been proposed to use a film mainly made of athermoplastic resin as an inner liner for a pneumatic tire as described,for example, in Japanese patent application Kokai publication No.2009-241855. For actual use of such a film, a manufacturing method isgenerally employed in which the laminated sheet including the film and atie rubber sheet cured and adhered to the film are wound around a tiremaking drum and lap-spliced and are then subjected to a step ofcure-molding the tire.

Alternatively, a tire can be manufactured by pulling out and cutting thelaminated sheet, which includes the film mainly made of thethermoplastic resin and the tie rubber sheet and which has been woundinto a roll-shaped body, from the roll-shaped body by a desired length,and winding the laminated sheet around the tire making drum. The processfurther includes lap-splicing the laminated sheet on the drum or thelike, and then cure-molding the laminated sheet. In this case, after thetire starts to be used for running, delamination may occur between thefilm mainly made of the thermoplastic resin, which constitutes the innerliner, and the tie rubber sheet that has been cured and adhered to thefilm.

To further illustrate this, as shown in FIG. 5( a), a laminated sheet 1including a film 2 mainly made of a thermoplastic resin and a tie rubberlayer 3 is cut into a predetermined size (length) with an edge tool orthe like. Then, both end portions of the laminated sheet 1 areoverlapped with each other and lap-spliced on a tire making drum in sucha way that a lap-splice portion S is provided and the laminated sheet 1forms an annular shape. When one laminated sheet 1 is used, both endportions thereof are lap-spliced in such a way that laminated sheet 1forms an annular shape. Meanwhile, when a plurality of laminated sheets1 are used, corresponding end portions of the laminated sheets 1 arelap-spliced and joined together in such a way that the laminated sheets1 form one annular shape as a whole.

Then, other parts (not illustrated) necessary for manufacturing the tireare wound and cure-molding is performed with a bladder. As a result ofthe cure-molding, the film 2 mainly made of the thermoplastic resinforms an inner liner layer 10 as shown in the view in FIG. 5( b) as amodel. Around the lap-splice portion S, there are formed a portion wherethe film 2 mainly made of the thermoplastic resin is exposed and aportion where the film 2 is embedded in the tie rubber layer. That is,in FIGS. 5( a) and 5(b), an upper side is a tire inner cavity side. Inother words, there is formed a pneumatic tire T which has the lap-spliceportion S where the end portions of the film 2 in the tirecircumferential direction overlap each other in the tire widthwisedirection with the tie rubber therebetween and in which the lap-spliceportion S exists extending in the tire widthwise direction.

The phenomenon of delamination between the aforementioned film 2 mainlymade of the thermoplastic resin and the tie rubber sheet 3 cured andadhered to the film 2 occurs particularly in a vicinity 4 of the tip orthe like of the film 2 at a spot shown in FIG. 5( b) where the film 2mainly made of the thermoplastic resin is exposed. In the beginning, acrack develops, and then grows into the sheet delamination phenomenon.

SUMMARY

In view of the above-mentioned circumstance, an object of the presentinvention is to provide a pneumatic tire in which an inner linerincluding a film mainly made of a thermoplastic resin is attached to aninside of the tire via a tie rubber sheet, on an inner side of a carcasslayer, and which has a lap-splice portion where end portions of the filmin a tire circumferential direction overlap each other in a tirewidthwise direction with tie rubber therebetween. Therefore, thepneumatic tire has no crack developing around a lap-splice portion ofthe inner liner layer after the pneumatic tire starts to be used forrunning, and thus has excellent durability.

In order to achieve the above object, the present invention provides apneumatic tire according to disclosed embodiments. One embodimentprovides a pneumatic tire in which an inner liner including a filmmainly made of a thermoplastic resin is attached to an inside of thetire via a tie rubber sheet, on an inner side of a carcass layer, andwhich has a lap-splice portion where end portions of the film in a tirecircumferential direction overlap each other in a tire widthwisedirection with tie rubber therebetween. Also, in the pneumatic tire, asection of the film on a tire cavity side in the lap-splice portion hasa portion where the film is thin over part or entirety of the width inthe tire widthwise direction, before the lap-splice portion.

Also, in the pneumatic tire according to this embodiment, acircumferential-direction overlap length of the lap-splice portion is 3to 30 mm, a tire-circumferential-direction length of the portion wherethe film is thin is 0.1 to 10 mm, and a thickness of the portion wherethe film is thin is 20% to 80% of a thickness T of the film. Also, thefilm is thin over part of the width in the tire widthwise direction,before the lap-splice portion, and the portion where the film is thinexists at least in a region between a belt end portion and a tip of abead filler portion in a cross section along a tire meridian line.

Another embodiment provide a pneumatic tire in which an inner linerincluding a film mainly made of a thermoplastic resin is attached to aninside of the tire via a tie rubber sheet, on an inner side of a carcasslayer, and which has a lap-splice portion where end portions of the filmin a tire circumferential direction overlap each other in a tirewidthwise direction with tie rubber therebetween. Also, at least one ofa section of the film on a tire cavity side and a section of the film ona tire outer circumference side in the lap-splice portion is formed insuch a way that a film thickness in the lap-splice portion is smallerthan a film thickness in a portion other than the lap-splice portion.

Furthermore, in the pneumatic tire according to this embodiment, aportion of the lap-splice portion which is formed to be thinner than afilm thickness of the portion other than the lap-splice portion isformed to have such a shape that the film becomes thinner stepwise, anda film thickness of the portion of the lap-splice portion where the filmis thin is 20 to 80% of the thickness of the film in the portion otherthan the lap-splice portion. Also, an overlap length of the lap-spliceportion in the circumferential direction is 3 to 30 mm. Furthermore, theportion of the lap-splice portion which is formed to be thinner than afilm thickness of the portion other than the lap-splice portion existsat least in a region between a belt end portion and a tip of a beadfiller portion in a cross section along a tire meridian line.

Accordingly, as will be described in more detail herein, after thepneumatic tires according to the disclosed embodiments start to be usedfor running a vehicle, no delamination occurs between the film mainlymade of the thermoplastic resin which constitutes the inner liner andthe tie rubber sheet cured and adhered to the film mainly made of thethermoplastic resin. The pneumatic tire therefore have excellent runningdurability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1( a) and 1(b) illustrate a portion of a pneumatic tire accordingto a disclosed embodiment in which a section of a film on a tire cavityside in a lap-splice portion has a portion where the film is thin overpart or entirety of the width in the tire widthwise direction, beforethe lap-splice portion, with FIG. 1( a) being a side cross-sectionalview around the lap-splice portion, and FIG. 1( b) being a plan view ofthe lap-splice portion;

FIGS. 2( a), 2(b) and 2(c) are cross-sectional views around thelap-splice portion of different configurations of the pneumatic tire asshown in FIGS. 1( a) and 1(b);

FIGS. 3( a) and 3(b) illustrate a portion of a pneumatic tire accordingto another disclosed embodiment, with FIG. 3( a) being a sidecross-sectional view around the lap-splice portion, and FIG. 3( b) beinga plan view of the lap-splice portion;

FIGS. 4( a), 4(b) and 4(c) are cross-sectional views around thelap-splice portion of different configurations of the pneumatic tire asshown in FIGS. 3( a) and 3(b);

FIGS. 5( a) and 5(b) are cross-sectional views for illustrating adisadvantage of a conventional pneumatic tire, with FIG. 5( a) showingthe state where a laminated sheet 1 obtained by laminating a film 2mainly made of a thermoplastic resin and rubber 3 cured and adhered tothe film mainly made of the thermoplastic resin is cut into apredetermined length and wound around a tire making drum, and then bothend portions of the laminated sheet 1 are lap-spliced, and FIG. 5( b)showing the state after the laminated sheet 1 has been cure-molded inthe state as shown in FIG. 5( a);

FIG. 6 is a partial cutaway perspective view showing an example of anembodiment of the pneumatic tire as shown in FIGS. 1( a) and 1(b);

FIG. 7 is a partial cutaway perspective view showing an example of anembodiment of the pneumatic tire as shown in FIGS. 3( a) and 3(b); and

FIG. 8 is a cross-sectional view taken along a tire meridian line whichis used to explain the pneumatic tire of the embodiments disclosedherein, and shows, as an example, regions in the film mainly made of thethermoplastic resin constituting the inner liner where it is preferableto provide a thin portion at least before the lap-splice portion, in thestate where the lap-splice portion exits over the entire width in a tirewidthwise direction E.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will now be explained withreference to the drawings. Description is given of materials of an innerliner which is a matter common to all of the embodiments.

As shown in FIGS. 1( a) and 1(b), in a pneumatic tire according to oneembodiment, an inner liner 10 including a film 2 mainly made of athermoplastic resin is attached to an inside of the tire via a tierubber sheet 3, on an inner side of a carcass layer 14 as shown in FIGS.6 and 8. Moreover, the pneumatic tire has a lap-splice portion S whereend portions of the film 2 in a tire circumferential direction overlapeach other in the tire widthwise direction with tie rubber 3′therebetween. The pneumatic tire is characterized in that a section ofthe film 2 on a tire cavity side in the lap-splice portion S has aportion 5 where the film 2 is thin over part or entirety of the width inthe tire widthwise direction, before the lap-splice portion S.

Various studies have been made on causes of delamitation between thefilm 2 mainly made of the thermoplastic resin which constitutes theinner liner 10 and the tie rubber sheet 3 cured and adhered to the filmmainly made of the thermoplastic resin. The delamination is adisadvantage of the conventional method.

Specifically, the delamination is considered to occur as follows in thecase where the above-described laminated sheet 1 is prepared by a normalmethod. Around the lap-splice portion S of both ends of the laminatedsheet 1 shown in FIGS. 5( a) and 5(b), large stress occurs in the tierubber 3′ interposed between the end portions of the film 2 mainly madeof the thermoplastic resin and having large stiffness, with the endportions exiting above and below the tie rubber 3′. As a result, a crackdevelops in a vicinity 4 of tip portions of the film 2 mainly made ofthe thermoplastic resin. Then, the crack becomes larger and delaminationthereby occurs.

On the contrary, in the pneumatic tire as shown in FIGS. 1( a) and 1(b),the section of the film 2 on the tire cavity side in the lap-spliceportion S has the portion 5 where the film 2 is thin over part orentirety of the width length in the tire widthwise direction E-E, beforethe lap-splice portion S. When the laminated sheet 1 is prepared bybeing cut into a predetermined length, a film having the portion 5 wherethe film is thin over part or entirety of the width in the tirewidthwise direction E-E before the lap-splice portion S is prepared asthe film 2 mainly made of the thermoplastic resin.

Providing the portion 5 where the film 2 is thin over part or entiretyof the width in the tire widthwise direction E-E before the lap-spliceportion S facilitates bending at the portion 5 where the thickness issmall and drastically reduces the occurrence of peeling off. A pneumatictire excellent in durability can be thereby obtained. This exerts asignificant effect in preventing phenomenon of delamination between thefilm 2 mainly made of the thermoplastic resin and the tie rubber sheet 3cured and adhered thereto after the tire starts to be used for running.

It is important that the portion 5 where the film 2 is thin is providedbefore the lap-spliced portion S. If the portion 5 is provided inlap-spliced portion where the end portions of the film 2 overlap eachother, the section of the film 2 mainly made of the thermoplastic resinis restrained by the section of the film 2 mainly made of thethermoplastic resin on the lower side in the drawing and is therebydifficult to bend. Accordingly, it is difficult to obtain theaforementioned effect of reducing the occurrence of peeling off.

In the pneumatic tire as shown in FIGS. 1( a) and 1(b), acircumferential-direction overlap length L of the lap-splice portion Sis preferably 3 to 30 mm, a tire-circumferential-direction length W ofthe portion 5 where the film 2 is thin is preferably 0.1 to 10 mm, and athickness t of the portion 5 where the film 2 is thin is preferably 20to 80% of a thickness T of the film 2. If the circumferential-directionoverlap length L of the lap-splice portion S is smaller than 3 mm, it isdifficult for the lap-splice portion S to exert a joint effect as asplice portion. On the other hand, the circumferential-direction overlaplength L of the lap-splice portion S being larger than 30 mm causesdeterioration of the uniformity of the tire and is thus undesirable.Moreover, the tire-circumferential-direction length W of the portion 5where the film 2 is thin being smaller than 0.1 mm is undesirablebecause processing of accurately forming the portion 5 becomesdifficult. Meanwhile, the length W being larger than 10 mm isundesirable because the effect is not improved by a degree correspondingto the increased length W and, even worse, there is possiblydeterioration in air permeation preventing performance as the innerliner. A more preferable range of the tire-circumferential-directionlength W of the portion 5 where the film 2 is thin is 1 to 5 mm.

The values respectively of the circumferential-direction overlap lengthL of the lap-splice portion S and the tire-circumferential-directionlength W of the portion 5 where the film 2 is thin and the positionalrelationship of the portion 5 where the film 2 is thin are as follows.As shown in FIGS. 2( a) through 2(c) in various embodiments, thecircumferential-direction overlap length L of the lap-splice portion Sis a circumferential direction length of a portion where the endportions of the film 2 overlap each other, irrespective of the positionof the portion 5 where the film 2 is thin. Moreover, the technical ideais determining the tire-circumferential-direction length of the portionwhere the film 2 is thin over part or entirety of the width in the tirewidthwise direction, before the lap-splice portion S. Accordingly, thetire-circumferential-direction length W of the portion 5 where the film2 is thin refers to a configuration as shown in FIG. 2( a) when theportion 5 where the film 2 is thin exists partially overlapping thelap-splice portion S, a length W excluding a section where the portion 5overlaps the lap slice portion S, a configuration as shown in FIG. 2( b)when the portion 5 where the film 2 is thin exists without overlappingthe lap-splice portion S, an entire length W of the portion 5 where thefilm 2 is thin, or a configuration as shown in FIG. 2( c) when aplurality of portions 5 where the film 2 is thin exist and there are aportion 5 overlapping the lap-splice portion S and a portion 5 notoverlapping the lap-splice portion S, a total length of lengths of theportions 5 (51 and 52 in FIG. 2( c)) existing without overlapping thelap-splice portion S (part of the portions exiting without overlapping(W1+W2 in FIG. 2( c)).

Further details of the pneumatic tire as shown in FIGS. 1( a) through2(c) as shown in FIG. 6 which is a partial cutaway perspective viewshowing an example of an embodiment of a pneumatic tire. A pneumatictire T includes a side wall part 12 and a bead part 13 in a continuousfashion on each of the left and right sides of a tread part 11. Insidethe tire, a carcass layer 14 serving as the tire's framework is providedextending in the tire widthwise direction between the left and rightbead parts 13 and 13. Two belt layers 15 made of steel cords areprovided on the outer circumferential side of a portion of the carcasslayer 14 corresponding to the tread part 11. An arrow E indicates thetire widthwise direction and an arrow X indicates the tirecircumferential direction. The inner liner layer 10 is disposed on theinner side of the carcass layer 14, and the lap-splice portion S thereofexists extending in the tire widthwise direction.

In the pneumatic tire as shown, the development of a crack on the tire'sinner circumferential surface around the lap-splice portion S, which islikely to develop in the conventional case, is suppressed. Moreover, thedevelopment of a crack and the occurrence of delamination between thefilm 2 mainly made of the thermoplastic resin which constitutes theinner liner layer 10 and the tie rubber layer 3, are suppressed. Thus,durability is significantly improved. The overlap length L of thelap-splice portion S is preferably 5 to 10 mm, depending on the tiresize.

Also in the pneumatic tire, the splice portion S formed by overlappingexists over the entire tire width. However, the portion 5 where the film2 is thin is not required to be provided over the entire width of thesplice portion S. It is preferable that the portion 5 exists, in thetire widthwise direction, at least in regions each from one end portionof a belt 15 b having a larger width to a front end portion of acorresponding one of bead fillers 16 which are denoted by Z in FIG. 8.Deformation is large particularly around shoulder portions duringrunning and crack and delamination of the tie rubber are thereby likelyto occur. Hence, it is preferable that the portion 5 is provided atleast in the regions Z including side wall portions. In other words, theportion 5 where the film 2 is thin is not required to continuouslyextend to exist over the entire width in the tire widthwise directionand may exist only over part of the width in the tire widthwisedirection. When the portion 5 exists, it is preferable that the portion5 exists at least in the region Z each from the end portion of the belt15 b having a larger width to the front end portion of the correspondingbead filler 16.

As mentioned above, FIGS. 3( a) and 3(b) illustrate a pneumatic tire ofanother embodiment. In the pneumatic tire, an inner liner 10 including afilm 2 mainly made of a thermoplastic resin is attached to an inside ofthe tire via a tie rubber sheet 3, on an inner side of a carcass layer14 as shown in FIGS. 7 and 8. Moreover, the pneumatic tire has alap-splice portion S where end portions of the film 2 in a tirecircumferential direction overlap each other in the tire widthwisedirection with tie rubber 3′ therebetween. The pneumatic tire ischaracterized in that at least one of a film section 2A on a tire cavityside and a film section 2B on a tire outer circumference side in thelap-splice portion S is formed in such a way that a film thickness inthe lap-splice portion S is smaller than a film thickness in a portionother than the lap-splice portion S. In FIGS. 1( a) and 1(b), referencenumeral 5 denotes a film portion formed to be thin. In the embodimentshown in FIGS. 3( a) and 3(b), both of the film section 2A on the tirecavity side and the film section 2B on a tire outer circumference sideare formed to be thinner than the film thickness in the portion otherthan the lap-splice portion.

As mentioned in the description of the embodiment shown in FIGS. 1( a)and 1(b), the delamination is considered to occur as follows in the casewhere a laminated sheet 1 is prepared by a normal method. Around thelap-splice portion S of both ends of the laminated sheet 1 shown inFIGS. 5( a) and 5(b), large stress occurs in the tie rubber 3′interposed between both end portions of the film 2 mainly made of thethermoplastic resin and having large stiffness, the end portionsexisting above and below the tie rubber 3′. As a result, a crackdevelops in a vicinity 4 of tip portions of the film 2 mainly made ofthe thermoplastic resin. Then, the crack becomes larger and delaminationthereby occurs.

On the other hand, in the embodiment shown in FIGS. 3( a) and 3(b), atleast one of the upper and lower film sections is the film portion 5formed to be thin, in the lap-splice portion S. Accordingly, thestiffness of the entire lap-splice portion S is reduced and thisfacilitates bending of the lap-splice portion S as a whole. Hence,occurrence of peeling off and delamination between the film and the tierubber can be drastically reduced and a pneumatic tire excellent indurability can be thereby obtained. This exerts a significant effect inpreventing phenomenon of delamination between the film 2 mainly made ofthe thermoplastic resin and the tie rubber sheet 3 cured and adheredthereto after the tire starts to be used for running.

In the lap-splice portion S, the film portion 5 formed to be thinnerthan the film thickness of the portion other than the lap-splice portionhas such a shape that a shape of a cross section along the tirecircumferential direction X-X gradually becomes thinner toward the tipas shown in FIG. 4( a), or such a shape that the shape of the crosssection becomes thinner stepwise as shown in FIGS. 4( b) and 4(c).Although the stepwise shapes shown in FIGS. 4( b) and 4(c) each have onestep, multiple steps may be provided.

Moreover, only the film section 2A on the tire inner cavity side may beformed to be thin as shown in FIG. 4( b) or only the film section 2B onthe tire outer circumferential side may be formed to be thin as shown inFIG. 4( c). Thus, in a case of thinning only one of the film sections,it is preferable to thin the film section 2A on the tire inner cavityside as shown in FIG. 4( b). This is considered to be because a largereffect of reduction in stiffness is obtained by thinning the filmsection located in a surface, and peeling off and delamination arethereby less likely to occur.

Processing of thinning the film is performed in a stage where the filmis a single body and is not laminated with the tie rubber sheet yet, byperforming, for example, laser processing in the tire widthwisedirection. In some cases, properties of a film surface are modified bythe laser processing and adhesiveness to the tie rubber sheet therebydeteriorates. In such case, it is preferable to thin the film byperforming the laser processing on a surface which is not to be broughtinto contact with the tie rubber sheet. Description is givenspecifically by using the embodiment shown in FIG. 4( b). In theembodiment shown in FIG. 4( b), the film section 2A on the tire innercavity side is thinned and the thinning is performed on a surface of thefilm section 2A on the tie rubber sheet side. In the case where theadhesiveness of the processed surface deteriorates by the processing ofthinning, it is preferable to perform thinning on a surface on the innercavity side which is opposite to the surface on the tie rubber sheetside. On the other hand, when the adhesiveness of the processed surfaceimproves by the processing of thinning, it is preferable to set thesurface on the tie rubber sheet to the surface to be processed to bethin because the effect of preventing the peeling off and delaminationcan be improved.

In the case of thinning the film stepwise as described above, athickness t of the film formed to be thin in the lap-splice portion ispreferably 20 to 80% of a thickness Tf of the film in the portion otherthan the lap-splice portion (FIG. 3( a) and FIGS. 4( b) and 4(c)). Ifthe film is thinned excessively, an excellent air permeation preventingperformance as the inner liner cannot be obtained and moldingworkability also deteriorates. The thickness t being larger than 80% ofthe thickness Tf is undesirable because the effect of reduction instiffness is small and it becomes difficult to obtain a desired effect.

In the pneumatic tire as shown in FIGS. 3( a) and 3(b), the overlaplength L of the lap-splice portion S in the tire circumferentialdirection shown is preferably 3 to 30 mm. If thecircumferential-direction overlap length L of the lap-splice portion Sis smaller than 3 mm, it is difficult for the lap-splice portion S toexert a joint effect as a splice portion. On the other hand, thecircumferential-direction overlap length L of the lap-splice portion Sbeing larger than 30 mm may cause deterioration of the uniformity of thetire and is thus undesirable. The preferable dimensions are the same asthose in the pneumatic tire shown in FIGS. 1( a) and 1(b).

Moreover, the film portion 5 where the film 2 is thin is preferablyformed to have a tire-circumferential-direction length almost equal tothe overlap length L. Specifically, the tire-circumferential-directionlength is preferably within a range of plus/minus 15% of the length L,more preferably within a range of plus/minus 10% of the length L.

As shown in more detail in FIG. 7, pneumatic tire T includes a side wallpart 12 and a bead part 13 in a continuous fashion on each of the leftand right sides of a tread part 11. Inside the tire, a carcass layer 14serving as the tire's framework is provided extending in the tirewidthwise direction between the left and right bead parts 13 and 13. Twobelt layers 15 made of steel cords are provided on the outercircumferential side of a portion of the carcass layer 14 correspondingto the tread part 11. An arrow E indicates the tire widthwise directionand an arrow X indicates the tire circumferential direction. The innerliner layer 10 is disposed on the inner side of the carcass layer 14,and the lap-splice portion S thereof exists extending in the tirewidthwise direction.

In the pneumatic tire, the development of a crack on the tire's innercircumferential surface around the lap-splice portion S, which is likelyto develop in the conventional case, is suppressed. Moreover, thedevelopment of a crack and the occurrence of delamination between thefilm 2 made mainly of the thermoplastic resin, which constitutes theinner liner layer 10 and the tie rubber layer 3, are suppressed. Thus,durability is significantly improved.

The splice portion S formed by overlapping exists over the entire tirewidth. However, the portion 5 where the film 2 is thin is not requiredto be provided over the entire width of the splice portion. It ispreferable that the portion 5 exists, in the tire widthwise direction,at least in regions each from one end portion of a belt 15 b having alarger width to a front end portion of a corresponding one of beadfillers 16 which are shown as regions Z in FIG. 8. Deformation is largeparticularly around shoulder portions during running and crack anddelamination of the film and the tie rubber are thereby likely to occur.Hence, it is preferable that the portion 5 is provided at least in theregions Z including side wall portions. This is the same as in thepneumatic tire as shown in FIGS. 1( a) and 1(b).

As can be appreciated from the description herein, the film mainly madeof the thermoplastic resin constituting the inner liner typically refersto a film made of a thermoplastic resin or a film made of athermoplastic resin composition obtained by blending a thermoplasticresin and an elastomer with the thermoplastic resin being a maincomponent. The same film is used in the embodiments discussed herein.Particularly, even in the case where the film is made of thethermoplastic resin composition obtained by blending the thermoplasticresin and the elastomer with the thermoplastic resin being the maincomponent, the main component is the thermoplastic resin. The filmmainly made of the thermoplastic resin has such a characteristic thatthe stiffness thereof is generally larger than that of a sheet made of100% rubber.

In this regard, in order to increase the life the pneumatic tire, it isextremely important to employ a configuration in which a portion of theinner liner around the splice portion is protected, as theconfigurations of the pneumatic tires described herein. Examples of thethermoplastic resin usable in the pneumatic tires include:polyamide-based resins [for example, nylon 6 (N6), nylon 66 (N66), nylon46 (N46), nylon 11 (N11), nylon 12 (N12), nylon 610 (N610), nylon 612(N612), nylon 6/66 copolymers (N6/66), nylon 6/66/610 copolymers(N6/66/610), nylon MXD6 (MXD6), nylon 6T, nylon 9T, nylon 6/6Tcopolymers, nylon 66/PP copolymers, and nylon 66/PPS copolymers]; theirN-alkoxyalkylates, for example, methoxymethylated nylon 6,methoxymethylated nylon 6/610 copolymers, and methoxymethylated nylon612; polyester-based resins [for example, aromatic polyesters such aspolybutylene terephthalate (PBT), polyethylene terephthalate (PET),polyethylene isophthalate (PEI), PET/PEI copolymers, polyarylate (PAR),polybutylene naphthalate (PBN), liquid crystal polyester, andpolyoxyalkylene diimide diacid/polybutylene terephthalate copolymers];polynitrile-based resins [for example, polyacrylonitrile (PAN),polymethacrylonitrile, acrylonitrile/styrene copolymers (AS),(meth)acrylonitrile/styrene copolymers, and(meth)acrylonitrile/styrene/butadiene copolymers];polymethacrylate-based resins [for example, polymethyl methacrylate(PMMA) and polyethylmethacrylate]; polyvinyl-based resins [for example,polyvinyl acetate, polyvinyl alcohol (PVA), vinyl alcohol/ethylenecopolymers (EVOH), polyvinylidene chloride (PVDC), polyvinyl chloride(PVC), vinyl chloride/vinylidene chloride copolymers, vinylidenechloride/methyl acrylate copolymers, and vinylidenechloride/acrylonitrile copolymers (ETFE)]; cellulose-based resins [forexample, cellulose acetate and cellulose acetate butyrate]; fluororesins[for example, polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF),polychlorofluoroethylene (PCTFE), and tetrafluoroethylene/ethylenecopolymers]; imide-based resins [for example, aromatic polyimide (PI)];and the like.

Moreover, any of the resins described above is usable as thethermoplastic resin out of the thermoplastic resin and the elastomerwhich can constitute the example of the thermoplastic resin compositionmainly made of the thermoplastic resin usable in the present invention.Meanwhile, examples of the preferably-usable elastomer include: dienerubbers and their hydrogenated products [for example, natural rubbers(NR), isoprene rubber (IR), epoxidized natural rubbers,styrene-butadiene rubber (SBR), butadiene rubbers (BR, high-cis BR andlow-cis BR), nitrile rubber (NBR), hydrogenated NBR, and hydrogenatedSBR]; olefin-based rubbers [for example, ethylene propylene rubbers(EPDM and EPM), maleic acid-modified ethylene propylene rubber (M-EPM),butyl rubber (IIR), copolymers of isobutylene and aromatic vinyl ordiene monomer, acrylic rubber (ACM), and ionomers]; halogen-containingrubbers [for example, Br-IIR, CI-IIR, brominatedisobutylene-co-para-methylstyrene copolymers (BIMS), chloroprene rubber(CR), hydrin rubber (CHR), chlorosulfonated polyethylene rubber (CSM),chlorinated polyethylene rubber (CM), and maleic acid-modifiedchlorinated polyethylene rubber (M-CM)]; silicone rubbers [for example,methyl vinyl silicone rubber, dimethyl silicone rubber, andmethylphenylvinyl silicone rubber]; sulfur-containing rubbers [forexample, polysulfide rubber]; fluororubbers [for example, vinylidenefluoride-based rubbers, fluorine-containing vinyl ether-based rubbers,tetrafluoroethylene-propylene-based rubbers, fluorine-containingsilicone-based rubbers, and fluorine-containing phosphazene-basedrubbers]; thermoplastic elastomers [for example, styrene-basedelastomers, olefin-based elastomers, ester-based elastomers,urethane-based elastomers, and polyamide-based elastomers]; and thelike.

At the time of blending in a combination of a specific one of theabove-mentioned thermoplastic resins and a specific one of theabove-mentioned elastomers, an appropriate compatibilizer may be used asa third component to make the thermoplastic resin and the elastomercompatible with each other if they are incompatible with each other. Theinterfacial tension between the thermoplastic resin and the elastomerdecreases when such a compatibilizer is mixed in the blend system. As aresult, the size of elastomer particles constituting the dispersionphase becomes finer. Accordingly, these two components exhibit theircharacteristics more effectively. In general, such a compatibilizer mayhave a copolymer structure including both or either of a structure ofthe thermoplastic resin and a structure of the elastomer, or a copolymerstructure including an epoxy group, a carbonyl group, a halogen group,an amino group, an oxazoline group, a hydroxyl group, or the like, whichis capable of reacting with the thermoplastic resin or the elastomer.Such a compatibilizer may be selected depending on the types of thethermoplastic resin and the elastomer with which the compatibilizer isblended. Examples of the compatibilizer normally used include:styrene/ethylene-butylene-styrene block copolymers (SEBS) and theirmaleic acid-modified products; EPDM; EPM; EPDM/styrene orEPDM/acrylonitrile graft copolymers and their maleic acid-modifiedproducts; styrene/maleic acid copolymers; reactive phenoxine; and thelike. The blending proportion of such a compatibilizer is notparticularly limited, yet the blending proportion is preferably 0.5 to10 parts by weight per 100 parts by weight of the polymer components(the total amount of the thermoplastic resin and the elastomer).

In the thermoplastic resin composition obtained by blending athermoplastic resin and an elastomer, the composition ratio of thespecific thermoplastic resin to the specific elastomer is notparticularly limited. This composition ratio may be set as appropriatein such a way that the thermoplastic resin is the main component and thethermoplastic resin composition has a structure in which the elastomeris dispersed as a discontinuous phase in the matrix of the thermoplasticresin.

In the pneumatic tires, the film mainly made of the thermoplastic resinmay be mixed with other polymers such as the compatibilizer, as long asthe other polymers do not impair the characteristics needed for theinner liner. The purposes of mixing such other polymers are to improvethe compatibility between the thermoplastic resin and the elastomer, toimprove molding processability of the materials, to improve heatresistance, to reduce costs, and so on. Examples of materials used forsuch other polymers include polyethylene (PE), polypropylene (PP),polystyrene (PS), ABS, SBS, polycarbonate (PC), and the like. Inaddition, a filler (calcium carbonate, titanium oxide, alumina, or thelike) generally blended in the polymer blend, a reinforcing agent suchas carbon black and white carbon, a softener, a plasticizer, aprocessing aid, a pigment, a dye, an antioxidant, and the like may beblended optionally as long as the blended materials do not impair thecharacteristics needed for the inner liner. The thermoplastic resincomposition has a structure in which the elastomer is dispersed as adiscontinuous phase in the matrix of the thermoplastic resin. Havingsuch a structure, this thermoplastic resin composition can provide theinner liner both with sufficient flexibility and with sufficientstiffness based on the effect of a resin layer as a continuous phase. Atthe same time, when this thermoplastic resin composition is molded, thethermoplastic resin composition can achieve the molding processabilityequivalent to that of the thermoplastic resin, regardless of the amountof the elastomer. The Young's modulus of each of the thermoplastic resinand the elastomer usable in the pneumatic tires is not particularlylimited, yet is set preferably to 1 to 500 MPa and more preferably to 50to 500 MPa.

EXAMPLES

Hereinbelow, the pneumatic tires described herein will be specificallydescribed with reference to examples.

Note that evaluated characteristics were measured by the methodsdescribed below.

(1) Evaluation of Delamination Resistance in Splice Portion:

Running test was performed for each of test tires (10 tires prepared foreach of Examples and Conventional Examples) for 80 hours by using a drumtesting machine under such a condition that an inflation pressure was120 kPa, a load was 7.24 kN, and a speed was 81 km/h. Thereafter,presence and absence of development of a crack and delamination of thetie rubber around the splice portion of the inner liner layer of theinner cavity were observed for each test tire.

The evaluation was performed in such a method that Conventional Example1 and Examples 1 to 6 related to the first embodiment were evaluated andcategorized into three levels of “excellent,” “normal,” and “notacceptable.” Moreover, evaluation of Conventional Example 11 andExamples 11 to 17 related to the embodiments described with regard toFIGS. 3( a) through 4(c) was performed with the delamination resistanceof Conventional Example 11 taken as an index of 100. A larger indexmeans better delamination resistance.

(2) Evaluation of Air Leakage:

Each of the test tires was mounted on a rim and inflated to 230 kPa.Thereafter, the test tire was left for one month to calculate a leakagerate of air pressure. In the evaluation, the air leakage resistance ofeach of Conventional Example 1 and Examples 1 to 6 related to theembodiment described with regard to FIGS. 1( a) through 2(c) wasindicated in an index with the air leakage resistance of the tire ofConventional Example 1 taken as an index of 100. The air leakageresistance of each of Conventional Example 11 and Examples 11 to 17related to the second invention was indicated in an index with the airleakage resistance of the tire of Conventional Example 11 taken as anindex of 100. A larger index means better air leakage resistance. Anindex greater by 5% is judged as better.

(3) Evaluation of Uniformity:

The evaluation was performed by measuring RFV (Radial force variation)according to JASO(Japanese Automotive Standards Organization) C-607-87.

The number of samples was ten and the uniformity of each of ConventionalExample 1 and Examples 1 to 6 related to the embodiment described withregard to FIGS. 1( a) through 2(c) was indicated in an index with theuniformity of the tire of Conventional Example 1 taken as an index of100. The uniformity of each of Conventional Example 11 and Examples 11to 17 related to the embodiment described in FIGS. 3( a) through 4(c)was indicated in an index with the uniformity of the tire ofConventional Example 11 taken as an index of 100. A larger index meansbetter uniformity. An index greater by 2% or more is judged as “better”and an index greater by 5% or more is judged as “significantly better.”

Examples 1 to 6 and Conventional Example 1

Examples 1 to 6 and Conventional Example 1 are related to the pneumatictire of the embodiment described with regard to FIGS. 1( a) through2(c). As each of test tires, a test tire having a tire size of 195/65R1591H (15×6J) and having a tire structure with two belt layers and twocarcass layers was prepared. Ten tires were prepared for each ofExamples and Conventional Example. In each of the test tires, a filmhaving a thickness (Tf) of 130 μm and made of N6/66 as the thermoplasticresin was used as the film mainly made of the thermoplastic resin andconstituting the inner liner. The making of the tire was performed insuch a way that the lap-splice portion S had the structure shown in FIG.1 and that the portion 5 where the film 2 was thin over the entire widthin the tire widthwise direction was provided before the lap-spliceportion S to be almost in contact with an end portion of the lap-spliceportion.

As shown in Table 1, Examples 1 to 6 were varied in thecircumferential-direction overlap length L of the lap-splice portion andthe tire-circumferential-direction length W of the portion 5 where thefilm was thin. The Conventional Example 1 was an example in which thefilm mainly made of the thermoplastic resin and constituting the innerliner was provided with particularly no portion 5 where the film wasthin.

In each of Examples 1 to 6, the thickness t of the portion 5 where thefilm (inner liner) is thin was 70 μm. The evaluation results of eachtest tire are shown in Table 1. As can be seen from these results, thepneumatic tire of the embodiment described with regard to FIGS. 1( a)through 2(c) is excellent in delamination resistance of the spliceportion, air leakage resistance, and uniformity.

TABLE 1 Conventional Example 1 Example 1 Example 2 Example 3 Example 4Example 5 Example 6 Circumferential- 7 7 7 7 7 2 40 direction overlaplength L of lap- splice portion (mm) Tire- 0 0.1 0.5 3 10 20 5circumferential (null) direction length W of portion where film is thin(mm) Delamination excellent normal excellent excellent excellent normalexcellent resistance to excellent Air leakage 100 100 100 99 95 94 99resistance Uniformity 100 100 100 100 100 103 94

Examples 11 to 17 and Conventional Example 11

Examples 11 to 17 and Conventional Example 11 are related to thepneumatic tire described with regard to FIGS. 3( a) through 4(c). As ofeach test tires, a test tire having a tire size of 195/65R15 91H (15×6J)and having a tire structure with two belt layers and two carcass layerswas prepared. Ten tires were prepared for each of Examples 11 to 17 andConventional Example 11. In each of the test tires, a film having athickness of 130 μm and made of N6/66 as the thermoplastic resin wasused as the film mainly made of the thermoplastic resin and constitutingthe inner liner.

The film of each of Examples 11 to 17 was cut into a desired length anda desired width and was thinned as described in the specifications shownin Table 2 by performing processing of repeatedly exposing both endportions of the film in the tire circumferential direction to a laserbeam in the tire widthwise direction. The conventional example 11 was anexample provided with particularly no portion where the film was thin.

Table 2 shows, for each of the lap-splice portions S, the length of thelap-splice (L mm), the side cross-sectional shape around the lap-spliceportion, and a ratio of the thickness t of the thinned portion to thethickness Tf (130 μm) of the film which is expressed in percent (%). Theevaluation result of dilamination resistance of the splice portion andthe evaluation result of uniformity are shown in Table 2 for each of thetest tires. As can be seen from these results, the pneumatic tire of theembodiment described with regard to FIGS. 3( a) through 4(c) isexcellent in delamination resistance of the splice portion and inuniformity.

TABLE 2 Conventional Example Example Example Example Example ExampleExample Example 1 11 12 13 14 15 16 17 Circumferential- 7 7 7 7 40 2 7 7direction overlap length L of lap-splice portion (mm) Side cross- FIG.5(b) FIG. 3(a) FIG. 4(b) FIG. 4(c) FIG. 3(a) FIG. 3(a) FIG. 3(a) FIG.3(a) sectional shape of lap-splice portion Thickness of 100 60 60 100 6060 10 90 film section 2A on cavity side in splice portion (at Tf (%))Thickness of 100 60 60 60 60 60 90 10 film section 2B on tire outercircumference side in splice portion (at Tf ratio (%)) Delamination 100108 105 105 105 102 101 101 resistance Uniformity 100 103 101 101 98 105100 100

General Interpretation of Terms

In understanding the scope of the present invention, the term“comprising” and its derivatives, as used herein, are intended to beopen ended terms that specify the presence of the stated features,elements, components, groups, integers, and/or steps, but do not excludethe presence of other unstated features, elements, components, groups,integers and/or steps. The foregoing also applies to words havingsimilar meanings such as the terms, “including”, “having” and theirderivatives. Also, the terms “part,” “section,” “portion,” “member” or“element” when used in the singular can have the dual meaning of asingle part or a plurality of parts. Also as used herein to describe theabove embodiment(s), the following directional terms “outboard”,inboard“, “forward”, “rearward”, “above”, “downward”, “vertical”,“horizontal”, “below” and “transverse” as well as any other similardirectional terms refer to those directions of a vehicle equipped withthe present invention. Accordingly, these terms, as utilized to describethe present invention should be interpreted relative to a vehicleequipped with the present invention. The terms of degree such as“generally”, “substantially”, “about” and “approximately” as used hereinmean a reasonable amount of deviation of the modified term such that theend result is not significantly changed. For example, two members thatare angled less than ten degrees apart would be considered “generallyperpendicular”, but two members that are angled more than fifteendegrees apart would not be considered “generally perpendicular”.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. For example, the size, shape, location ororientation of the various components can be changed as needed and/ordesired. Components that are shown directly connected or contacting eachother can have intermediate structures disposed between them. Thefunctions of one element can be performed by two, and vice versa. Thestructures and functions of one embodiment can be adopted in anotherembodiment. It is not necessary for all advantages to be present in aparticular embodiment at the same time. Every feature which is uniquefrom the prior art, alone or in combination with other features, alsoshould be considered a separate description of further inventions by theapplicant, including the structural and/or functional concepts embodiedby such feature(s). Thus, the foregoing descriptions of the embodimentsaccording to the present invention are provided for illustration only,and not for the purpose of limiting the invention as defined by theappended claims and their equivalents.

What is claimed is:
 1. A pneumatic tire comprising: a carcass layer; andan inner liner including a film including a thermoplastic resin that isattached to an inside of the tire via a tie rubber sheet on an innerside of the carcass layer, the inner liner having a lap-splice portionwhere end portions of the film in a tire circumferential directionoverlap each other in a tire widthwise direction with tie rubbertherebetween, a section of the film on a tire cavity side in thelap-splice portion having a portion where the film is thin over part orentirety of the width in the tire widthwise direction before thelap-splice portion, a circumferential-direction overlap length of thelap-splice portion being 3 to 30 mm, a tire-circumferential-directionlength of the portion where the film is thin being 0.1 to 10 mm, and athickness of the portion where the film is thin being 20% to 80% of athickness of the film.
 2. The pneumatic tire according to claim 1,wherein the film is thin over part of the width in the tire widthwisedirection before the lap-splice portion; and the portion where the filmis thin exists at least in a region between a belt end portion and a tipof a bead filler portion in a cross section along a tire meridian line.3. The pneumatic tire according to claim 1, wherein the film is thinover the entirety of the width in the tire widthwise direction beforethe lap-splice portion.